9.4 Reactions in Cells

For thousands of years, people used whale oil and other animal fats as fuels for their lamps. As fats burn, they combine with oxygen and produce carbon dioxide and water. They also release energy in the form of heat and light. In a lamp, combustion takes place rapidly. In the cells of organisms, a more controlled version of the process releases energy stored in molecules. Some of the energy released helps maintain your internal body temperature at or close to 37°C.

Figure 18 Unlike a plant, this runner must get the energy he needs from the food he eats.

Reactions that take place in cells follow the same rules as reactions that take place in a research laboratory or classroom. Some reactions go to completion and some reach an equilibrium point. Many reactions occur in solution and catalysts are often needed. Energy is transferred and energy is converted from one form to another. Photosynthesis and cellular respiration are two processes that allow organisms to meet their energy needs.

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